The invention relates generally to visual image display systems and more particularly to a high speed digital image exchange system which supports a plurality of display devices for one or more computers, video terminals or graphic work stations.
The transmission of visual images or visual pattern data often requires considerable time because of the limited data-transmission speed normally possible over a conventional transmission line. For example, a typical video random access memory (VRAM) capable of storing one frame of video information comprising 512 .times.512 piccels having 4096 colors, must leave a storage capacity of about 3Mbits/frame. Transmitting 3Mbits (i.e., 3.times.10.sup.6 bits) of information would require about 5.5 minutes over a RS232C serial line which has 9600 bands transmission capacity, for example. Such a long transmission time is too long for an interactive operation system of a computer.
It is possible to improve transmission time by connecting each video terminal to a remote processor. However, this necessitates very complicated wiring and requires that strict limitations on cable lengths be observed, because of signal attenuation characteristics of cable. Furthermore, signal source selection is also greatly restricted, because of the need for physical cable switching or reconnection to accommodate selection from among multiple sources.